A study published Monday in the Journal of the American Medical Association found that people who cut their calories by 25 percent for two years not only lost weight, but also had better moods, sleep and sexual function.

This kind of dramatic calorie cutting is sometimes called calorie restriction or a fasting diet. Fasting diets have been gaining recognition as relatively safe ways to lose weight and improve health, generally by lowering insulin levels, which helps reduce the risk of diabetes, cancer, and heart disease. Researchers attributed the improvement in general quality of life (sex, sleep) to simply feeling better.

Fasting diets vary in format, but most result in a long-term, substantial calorie deficit, like the one studied. Intermittent fasting can work like like the popular 5:2 diet, which involves eating normally for five days and then restricting to 500 calories for two days. A University of Southern California study on mice found that restricting calories several days a week did reduce the risk of major diseases. It's also an effective way to lose weight because people who limit themselves to only 500 calories one day don't make up the difference the next day, even when they are free to eat whatever they want. On average, they only eat 15 percent more calories than usual. This results in a large calorie deficit overall.

Fasting diets are generally a repackaging or a reworking of the Calorie Restriction movement, which has been around for years. Calorie restriction has also been shown to increase lifespan in some animals, and in primates, it has been shown to increase the number of healthy years, but not overall lifespan.

The evidence in favor of intermittent fasting and calorie restriction should not be confused with "cleanses." The body has effective detoxification processes, and there's no evidence that drinking only juice for a week, for instance, helps the body cleanse itself.

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